arm64: head.S: ensure visibility of page tables

After writing the page tables, we use __inval_cache_range to invalidate
any stale cache entries. Strongly Ordered memory accesses are not
ordered w.r.t. cache maintenance instructions, and hence explicit memory
barriers are required to provide this ordering. However,
__inval_cache_range was written to be used on Normal Cacheable memory
once the MMU and caches are on, and does not have any barriers prior to
the DC instructions.

This patch adds a DMB between the page tables being written and the
corresponding cachelines being invalidated, ensuring that the
invalidation makes the new data visible to subsequent cacheable
accesses. A barrier is not required before the prior invalidate as we do
not access the page table memory area prior to this, and earlier
barriers in preserve_boot_args and set_cpu_boot_mode_flag ensures
ordering w.r.t. any stores performed prior to entering Linux.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Fixes: c218bca74eeafa2f ("arm64: Relax the kernel cache requirements for boot")
Signed-off-by: Will Deacon <will.deacon@arm.com>

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 51c9811e683c84bfe8cb4889e8eb5f00cea1ea37..bbc474cd0ca83ca9f668ac35a27fd8a35025fcd9 100644 (file)
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -458,6 +458,7 @@ __create_page_tables:
         */
        mov     x0, x25
        add     x1, x26, #SWAPPER_DIR_SIZE
+       dmb     sy
        bl      __inval_cache_range
 
        mov     lr, x27